The present invention relates generally to an apparatus to mix concrete and, more particularly, to a turbine cement/water mixing apparatus for premixing a cement slurry for use in the production of concrete.
Concrete trucks, such as is described in U.S. Pat. No. 3,310,293, issued to Harold M. Zimmerman on Mar. 21, 1967, and U.S. Pat. No. 4,406,548, issued to Paul M. Haws on Sep. 27, 1983, carry supplies, such as aggregate, cement and water, in discrete hoppers from which the supplies are drawn in predetermined ratios to be deposited in a mixing auger apparatus where the combined supplies are mixed and turned into concrete to be discharged from the mixing auger externally of the concrete truck. This mixing auger apparatus is formed from a generally semi-circular flexible housing against which a standard pitch, spiral flighted auger works to not only mix the combined supplies, but to convey the combined supplies, and ultimately the created concrete, to the remote discharge end of the auger.
Conventional ready-mix concrete production has utilized a rotatable drum mounted on a truck frame to deliver mixed concrete to a delivery site by discharging the mixed concrete from the elevated, rearwardly directed, central discharge opening of the drum. More recent variations of the conventional concrete mixers have reoriented the drum to position the discharge opening toward the front of the truck, which enables the operator to control the discharge and delivery of the mixed concrete through a front-mounted discharge chute mechanism without leaving the cab of the truck.
Concrete trucks, as described in the aforementioned U.S. Pat. Nos. 3,310,293 and 4,406,548, located the mixing auger apparatus at the rear of the truck to receive the respective supplies fed downwardly and rearwardly thereto. The upward incline of the mixing auger allowed the mixed concrete to be discharged from a slightly elevated position to be delivered through a cooperative discharge chute mechanism. A mere repositioning of the mixing auger apparatus to the front of the truck to enable the forward discharge of the mixed concrete forwardly thereof is not a simple design choice as the operator's cab of the truck prevents the relocation of the mixing auger apparatus to the opposing front position. The forwardly delivering concrete truck must be capable of delivering mixed concrete at a forward position above the cab of the truck so that a discharge chute mechanism, which must be storable in a transport position above the truck cab out of the line of sight of the operator, can deliver the mixed concrete to the ground forwardly of the truck.
The mobile concrete production system includes a storage tank mounted on the chassis bed which has two longitudinally extending hoppers separated by a common wall. One hopper contains sand, and the other contains gravel or stone. A central, longitudinal conveyor operatively mounted along a bottom trough common to both hoppers receives sand and stone and delivers the materials to a rear discharge end. Also, the system includes a separate cement hopper as well as a separate water tank mounted on the chassis. Cement is dispensed in the desired proportion by a metering mechanism from the cement storage hopper into the discharging sand and stone and all three ingredients are then delivered into a elongated mixing trough mounted on the rear of the chassis. Water is added with the materials at the entrance and the ingredients are mixed into concrete in the trough before being discharged from the trough at the job site.
Many advantages and benefits are enjoyed by persons who employ the mobile concrete system in their concrete production business. An important one is that the system permits the formulation and delivery of relatively continuous amounts of concrete which can be used to fulfill orders where only small quantities of concrete are needed, thus obviating the need for taking such quantities from a single large pre-mixed batch. Since only a small portion of the system, the mixing trough, is utilized for mixing the concrete, it can be quickly and easily cleaned after completion of a “mixing” or production operation. Equally important, since the mixing of the concrete is performed “on site”, selective variation of the ingredients of the mixture can be readily accomplished and the water content of the mixed concrete can be easily controlled. Finally, in the mixing trough, a positive mechanical mixing action at a desired rate is performed to assure a uniform dispersal of all the ingredients of the concrete mix.
The incorporation of cement into a concrete production system, whether a ready-mix batch system or a mobile system, typically involves the mixing of dry cement with the aggregate and water until the mixture is homogenous. Admixtures are often added to the mixture to accomplish desired functions, such as changing the set time, increasing temperature, adding color to the concrete mixture, incorporating air into the mixture, etc. In both batch and mobile concrete production systems, a certain percentage of individual cement particles remain unhydrated despite an aggressive mixing action and despite the incorporation of additives to improve the hydration of the cement. A more thorough hydration of the individual cement particles can lead to increase strength and reduce concrete set times.
Some concretes produced by the mobile production system encounters a phenomenon commonly referred to as “false set”, which can be described to as a premature stiffening of the concrete. This phenomenon is typically solved through the use of a specially formulated cement product that is more expensive than the cement used in batch production systems. Accordingly, the unit cost of mobile production concrete is higher than conventional batch production concrete. It would be desirable to provide a process that would improve the mobile production of concrete to permit the use of a conventional cement formulation without incurring the false set problems.
The production of concrete, whether via a mobile concrete system or a ready mix system, typically involves the placement of dry cement, dry aggregate and dry sand into a mixing apparatus where water is added to hydrate the cement and create concrete. Admixtures to entrain air, to increase strength, to increase hydration, to die the concrete, etc. are added to the mixture during the mixing operation. Full hydration of the cement is such operations is not possible, thus chemical additives for the produced concrete is normal.
It would, therefore, be desirable to provide an apparatus and an improved process for producing concrete by effecting a substantially complete hydration of the cement particles.